Cadmium Cementation Research Articles

Circulating Flow-Electric-Field-Configuration-Enhanced Cadmium Cementation from Sulfate Systems and Its Optimization Mechanism.

In this work, a novel flow-electric field coupling configuration was designed and implemented for enhancing Zn-Cd cementation. A series of tests was conducted to explore the optimization of the Zn-Cd cementation process and its mechanism. Firstly, the various characteristics of the sponge cadmium at various locations in the device were compared, and it was concluded that the optimum purity of the sponge cadmium obtained from the anode was up to 94.1%. The generation and stripping of the cadmium sponge was revealed for the first time by cross-sectional electron microscopy. The four stages of the apparent reaction in the system were analyzed in relation to the pH, cadmium concentration and cadmium sponge flaking at each flow rate. It was proved that the separation of cadmium sponge mainly occurred in the third phase. Secondly, by comparing the morphology and specific surface area of the cadmium sponge at different flow rates, the optimum flow field velocity was identified as 30 mL/s. At this point, the specific surface area reached a maximum of 1.151 m2/g. Six flow field configurations were compared and preferred. The results demonstrated that the LCAH (Low-Cathode-Anode-High) modulation resulted in a sparser structure of the cadmium sponge, which was more easily exfoliated from the zinc anode surface by fluid impact. This was considered to be the most beneficial flow field configuration for improving the cadmium cementation rate and reducing the cost of the reaction. Moreover, the reaction steps of the system were analyzed. Its rate-limiting step was initially empirically identified as the diffusion step and proven by calculating the activation energy of 12.6 kJ/mol. It was confirmed that the diffusion process under different flow field configurations followed the first-order kinetic principle. In addition, the system's reaction phases were compared. Calculations confirmed that the diffusion process under various flow field configurations followed first-order kinetics. The diffusion coefficient of LACH proved to be the highest in the comparative tests, and the evident experimental results supported this conclusion.

Study of cadmium ions cementation with zinc powder from high-cadmium-concentration zinc sulphate solutions

ABSTRACT The recovery of metals from industrial and metallurgical effluents is crucial to minimise the environmental and economic impacts associated with the generation and disposal of these solutions. Therefore, this study uses zinc powder for the cementation of cadmium from a high-cadmium-concentration zinc sulphate solution. This study investigates the dependence of cadmium removal efficiency on the initial copper concentration, solution pH, stoichiometric ratio of added zinc, temperature, particle size, zinc powder activation and mode of zinc addition. The results show the possibility of achieving a cadmium removal efficiency 90–95% under optimal conditions. The reaction kinetics calculations revealed an activation energy of 11.89 kJ mol–1, indicating a diffusion-controlled reaction mechanism and the possibility to reduce the limitations of the controlling step by increasing the stirring rate during the cementation process. These observations provide further understanding and guidance toward the efficient utilisation of cadmium cementation to prepare sponge cadmium in zinc hydrometallurgy.

Исследование кинетики цементации кадмия в присутствии ПАВ

The aim of the paper is to study the kinetics of cadmium cementation with zinc powder in aqueous media in a continuous mode using an ion-selective cadmium electrode. Reduction of cadmium from aqueous solutions was carried out with zinc powder, with particle sizes from 63 to 200 μm. In a number of experiments, the influence of the cationic flocculant Besfloc K6645 on the cadmium cementation process was tested. The process was carried out in the temperature range from 30 to 50 °C with continuous stirring at 200 rpm with an overhead stirrer. Kinetic curves were recorded using a cadmium-selective electrode. The kinetic curves were conditionally divided into linear segments. Tangents were drawn to each section, which made it possible to determine the apparent rate constants using the first-order equation, as well as the mode coefficients using the Erofeev–Kolmogorov equation. An increase in temperature had a positive effect on cementation. The introduction of a flocculant into the electrolyte in the amount of 70 mg/L reduced the degree of cementation from two to three times over a period of 600 s. The data obtained made it possible to calculate the activation energies of the process rates on the linear sections of the kinetic curves, which amounted to approximately 46, 32 and 11–13 kJ/mol in the first, second, and third sections, respectively, for reduction without the addition of a flocculant, as well as 117–130 and 82–85 kJ/mol in the presence of Besfloc K6645 flocculant. It has been shown that in the presence of a flocculant, the activation energy increases, especially in the first section, which is characterized by a slow cementation rate. The study demonstrates the effect of the Besfloc K6645 additive on the duration of the initial section of the cementation kinetic curves.

Study to enhance cementation of impurities from zinc leach liquor by modifying the shape and size of zinc dust

Cementation is a prominent purification technique used for removal of copper, cadmium, cobalt, and nickel from impure zinc sulphate solution obtained after leaching of zinc ore. Zinc dust is primarily used for this purpose still the extent of purification is limited. The present study represents the encouraging result in context to utilization of zinc dust for better purification by altering its dosage, size and morphology. The investigations showed that 300% excess zinc dust dosage than stoichiometric results in enhanced cement formation. The study also revealed that fine size and ball milling of zinc dust favors cementation. Zinc dust of −300 mesh (BSS) after 2 h ball milling highly purifies the impure solution within 2 h contact time. The yield of the impurities removal after the optimized cementation is 100, 99.99, 100 and 15% for Cu, Cd, Ni and Co respectively. The kinetics of cementation has been also studied and revealed that the reaction is in mixed controlled mechanism for copper and cadmium cementation. At the same time, for nickel, it is considered to be chemically controlled. The activation energy for the cementation of copper, cadmium and nickel were 38.19, 30.87 and 68.15 kJ /mol, respectively. The estimated activation energies were found within the range which corroborates with the mixed and reaction model and ensures industrial feasibility of the proposed process.

Impact of silica on cadmium cementation by zinc dust in a zinc SX/EW plant

Horsehead Metal Products is a zinc refinery in Mooresboro, NC, treating crude Waelz oxide (WOX) to produce special high-grade zinc by a hydrometallurgical process comprising leaching, zinc solvent extraction/electrowinning, melting and casting and bleed treatment. Cadmium removal by zinc-dust cementation plays an essential role in the bleed treatment circuit to prevent cadmium buildup in the circuit. Silica, though present at a low level of approximately 0.3 percent in the WOX feed material, had a significant impact on the efficiency of cadmium cementation with zinc dust, most likely due to the passivation of zinc dust particles with silica gel. Solid/liquid separation efficiency by filter press was also affected. To identify the source of the silica issues, silica levels were mapped throughout the circuit, and adjustments, including using pregnant leach solution as the feed to cementation, and pH control in the WOX leaching and neutralization were introduced to mitigate the issues created by silica gel in the circuit.

RECOVERY OF VALUABLE METALS FROM ZINC PLANT RESIDUE THROUGH SEPARATION BETWEEN MANGANESE AND COBALT WITH N-N REAGENT

Recovery and separation of cobalt and manganese from one of zinc plant residues (ZPR), namely hot filter cake (HFC) using a hydrometallurgical process was studied. The process is carried out in four steps as follows: (1) washing zinc, (2) reductive leaching with hydrogen peroxide, (3) cadmium cementation with zinc powder and (4) separation of cobalt from manganese with beta naphthol. In this research, the separation between manganese and cobalt from the HFC using N-N reagent was investigated. The influence of several parameters on the course of the reaction such as N-N quantity, pH, temperature and reaction time was also examined. The optimum separation conditions were found to be N-N quantity: 8 times of stoichiometric value, time: 30 min, temperature: 25 °C and pH = 1.5. Using the optimized conditions, the cobalt and manganese precipitation was nearly 99% and 0%, respectively. A kinetic study of manganese precipitation through N-N reagent has been carried out to assess the effect of kinetics parameters. The data obtained for the leaching kinetics indicated that the precipitation of manganese is an ash diffusion controlled reaction and the reaction activation energy is equal to 1.4kJ/mol.

Recovery of zinc from Cd–Ni zinc plant residues

As the scope of the present work, zinc which is engaged in Cd–Ni zinc plant residues has been successfully recovered. While zinc contained in Cd–Ni filtercake has a considerable economic value, cadmium present in the material is one of the major sources of cadmium contamination of the environment. A novel hydrometallurgical technique was utilized for the separation of zinc from cadmium and nickel. Moreover, high purity cadmium and nickel were advantageously separated in successive cementation stages which in turn served as an environmental breakthrough. The process was composed of the collective leaching of the filtercake in order to bring as much metal as possible into the solution followed by selective cementation of cadmium and nickel, respectively. Therefore, a stock solution was provided under the optimum leaching conditions being as t = 150 min, T = 45 °C, stirring speed = 500 rpm, S/L = 1/13, pH = 1.3–1.5 and then cadmium was separated through cementation with zinc plates while nickel was cemented using zinc powder. The optimum working conditions for cadmium cementation were found to be as T = 25 °C, t = 180 min, pH = 2–2.5, stirring speed = 20 rpm and active plate area = 100 cm 2/L, while those of nickel were as T = 80 °C, t = 15 min, pH = 3.9–4.1, stirring speed = 50 rpm and zinc powder amount equal to stoichiometric amount needed for the cementation of nickel. Under such conditions, 98.95% of cadmium and 99.98% of nickel were recovered from the solution. Finally, a simple and effective conceptual flow diagram was proposed for the process.

The selective recovery of cadmium(II) from sulfate solutions by a counter-current extraction–stripping process using a mixture of diisopropylsalicylic acid and Cyanex® 471X

The liquid–liquid extraction of cadmium(II) from solutions, obtained by leaching of deposited cadmium carbonate or cadmium cementation sponge and heavily contaminated with other components, especially zinc, has been studied. Initially the solutions were purified; iron and other contaminants were removed by oxyhydrolysis. An equimolar mixture of diisopropylsalicylic acid and Cyanex® 471X (0.5 mol/L/0.5 mol/L), diluted with Solvesso 150, was used as the solvent. Experiments were performed both, as a laboratory simulation of a counter-current system, and in continuous counter-current trials using mixer-settlers. Good separation of cadmium(II) and zinc(II) has been obtained.

Effect of surfactants on the cementation of cadmium.

The cementation of cadmium ions (Cd(2+)) from aqueous solution onto zinc was studied in two batch reactors, a batch stirred reactor lined with a cylindrical zinc sheet and another that used a rotating zinc cylinder. The rate of cadmium removal was studied as a function of speed of rotation, initial cadmium concentration, and the addition of certain surfactants and their mixtures. Rotational speed and initial cadmium concentration affect the rate of cadmium cementation. It was found that sodium dodecyl sulfate (SDS) improves the rate of cadmium cementation, while Triton X-100 and cetyltrimethylammonium bromide (CTAB) inhibit it. Thermodynamic parameters were calculated and discussed. Visual observations showed that cadmium deposits on the zinc sheet are in the form of a powder, while cadmium deposits on the zinc cylinder, in the presence of SDS, give porous grains which increases the roughness of the surface, leading to an increase in the cementation rate. The lowest deposit porosity was observed in the presence of CTAB, which corresponds to the highest decrease obtained in the rate of cadmium cementation. The cementation process was successfully applied to recover Cd(2+) spiked into an industrial wastewater sample.

The influence of copper on the effect of certain surfactants during the cementation of cadmium by suspended zinc particles

The influence of copper on the effect of nonylphenolpolyethylene glycol (D1), dinaphthylmethane-4,4′-disulphonic acid (D2) and polyethylene glycol with molecular weight 400 (D3) during cadmium–zinc dust cementation was investigated. The behaviour of D1, D2 and D3 was determined by comparing the results obtained with and without surfactant. It was found that in the presence of copper D1 improves, but D2 and D3 inhibit cadmium cementation. The presence of copper substantially changes the effect of D1 and D3 which becomes opposite to the effect of these surfactants in the absence of copper. The addition of copper has no effect on the influence of D2. SEM study of cementation products indicates a change of deposit structure in the presence of copper. The addition of copper causes the formation of coarser deposits. Morphology of cementation products changes from a completely compact layer in the presence of D1 to a porous layer in the presence of both copper and D1 which corresponds to the cementation kinetics results. The addition of copper enhances dendrite formation in the presence of D2 and contributes to the formation of clusters in the presence of D3. Dendrite formation in the presence of D2 probably increases hydrogen evolution which inhibits cadmium deposition. The addition of D1 to the zinc sulphate solution containing copper and cadmium increases co-deposition of these impurities during the cementation by suspended zinc particles.

The effect of certain surfactants on the cementation of cadmium by suspended zinc particles

The effect of the surfactants nonylphenolpolyethylene glycol (D1), dinaphthylmethane-4,4′-disulphonic acid (D2) and polyethylene glycol with molecular weight 400 (D3) on cadmium-zinc dust cementation kinetics as well as on cadmium deposit structure was investigated. The behaviour of each surfactant was determined by comparing the results obtained with and without surfactant. The reaction of cadmium cementation follows first-order kinetics in the presence of and without surfactants. Additions D1 and D2 decrease but D3 increases the rate of cadmium deposition. Highest inhibition effect on the cementation rate was found in the presence of D1. The increase of cadmium deposition in the presence of D3 probably corresponds to the inhibition of hydrogen evolution due to the addition of this surfactant. SEM study of cadmium deposits showed the formation of a uniform layer of cadmium on the zinc particles surface in the presence of D1 and D3 as well as the formation of many dendrites in the presence of D2. The lowest deposit porosity is observed in the presence of D1 which correlates with the high inhibition effect of this surfactant on cadmium cementation rate. Dendrite formation in the presence of D2 probably increases hydrogen evolution which is in accordance with the obtained inhibition effect of D2 on cadmium cementation. Cadmium deposited in the presence of D3 forms a layer with a high porosity.

Purification of an ammoniacal zinc leach liquor using a rotating zinc disc after copper solvent extraction

A process for purifying an ammoniacal complex sulphide leach liquor through a cementation route using pure zinc is described. Purification of the leach liquor is mandatory in order to improve the quality of electrowon zinc. The cementation studies were carried out using a rotating zinc disc. Various parameters such as rotation speed and the effect of copper ion vis-à-vis the cementation of cadmium, cobalt and nickel were studied. The presence of copper gives a marked improvement in the cementation of cobalt and nickel whereas cadmium cementation shows a negative trend. With an increase of rotation speed of the zinc disc, the rate of cementation becomes faster. Initially the cementation rate is faster and with time the rate falls off. The cementation of cadmium is much faster than that of cobalt and nickel.

Examination of the Zinc Cementation of Cadmium in Aqueous Solutions

The kinetics of the cementation of cadmium by zinc have been studied over a range of solution pH values and initial cadmium concentrations. The kinetics were interpreted in terms of a model postulating a transition from a migration controlled mechanism with consequent half order kinetics to a diffusion controlled regime following first order kinetics. The conditions under which each mechanism was found to apply were consistent with the model in which the immediate reductant was hydride ion generated by the interaction of hydrogen ions with the zinc. The reaction stoichiometry was remarkable in that conditions were observed under which more than the theoretical one mole of cadmium per mole of zinc could be reduced. This was ascribed to the electrolysis of water by the induced electrochemical system. A lag in both cadmium cementation and zinc dissolution was observed in many runs. The zinc dissolution was found to commence about 25% sooner than cadmium cementation, a fact ascribed to the establishment of the reducing electrochemical system.

Cadmium Purification with a Vibrating Reactor

This paper describes the results of pilot plant testwork on a novel single stage zinc solution purification process using a vibratory reactor. This technique was modified for continuous cadmium cementation. There are distinct advantages to combining an intensely agitated reactor with a high mass of precipitant per unit volume in the form of granular zinc instead of zinc dust, including significant reduction of cementation agent consumption and substantial upgrading of the cadmium cement. This technique has the potential to minimize equipment, reduce plant size, and diminish operating costs.

Recovery of zinc from melting furnace residue

Slag from a zinc cathode melting furnace contains about 60% metallic zinc. This may be increased to 80–90% in the coarse size fractions (+200 mesh) by grinding and sieving. Residual zinc oxide may be removed by leaching with 5% H 2SO 4. Zinc recovery is about 77–84%. The zinc from the coarse size fractions may be melted for ingot production, whilst the finer material is suitable for cadmium cementation (−200 mesh material is similar to zinc dross). The process has been studied on both the laboratory and plant scales and process engineering indicates that it is economic.